Configuration file syntax

Please review it, especially the formal definition; and please use
in-line comments to note any problems.

Whilst doing that, I found out that Confluence has an "Excerpt" macro
that can mark part of the page content for reuse; and it has a "Children
Display" macro that can show the title and excerpt of child pages. So,
the contents of this page:

Re: Configuration file syntax

On Thu, Dec 6, 2018 at 5:50 PM Branko Čibej <[hidden email]> wrote:
...
> Whilst doing that, I found out that Confluence has an "Excerpt" macro
> that can mark part of the page content for reuse; and it has a "Children
> Display" macro that can show the title and excerpt of child pages. So,
> the contents of this page:
>
> https://cwiki.apache.org/confluence/x/6ojQBQ>
> are completely automatically generated and will be updated as we add new
> documents. Surely that's a great motivation to write them? :)

Awesome! It's nice to see our wiki documentation coming more and more
to life :-).

Thanks for all the documentation efforts (especially to you and Julian).